1. Field
The present embodiments generally relate devices, systems, methods and control systems for launching at least one boat from a structure that is at least partially surrounded by water. The present embodiments also concerns structures, such as an offshore installation or a sea-going vessel, comprising such a device or system and a computer program product.
2. Description of the Related Art
Many ships and offshore installations, such as oil platforms, are equipped with lifeboats to allow passengers and crew to escape in an emergency. Ship-launched lifeboats were traditionally designed to be lowered from davits on the ship's deck. A davit is a structure, such as a mechanical arm with a winch, which is used to lower lifeboats over the side of a ship.
Nowadays, many ships and offshore installations are provided with freefall lifeboats that are stored on a downward sloping launch ramp. When the lifeboat is released, it slides down the launch ramp and drops into the water. A disadvantage with freefall lifeboats is that if launched, return to the launching system is only possible using means such as a hydraulic lift since such lifeboats are considerably heavier than lifeboats that are designed to be lowered from davits, so as to survive the impact with water. Freefall lifeboats are however used for their capability to launch almost instantly and their high reliability.
Freefall lifeboats are designed to withstand a predetermined drop/launch height, usually in the range of 20-40 fmeters above sea level. A lifeboat that is launched from a launch ramp positioned at an optimum height will be propelled away from the structure on which the lifeboat ramp is mounted. However, if a launch ramp is mounted on a floating offshore structure, such as an oil platform, the height of the launch ramp above sea level may become too high or too low if the structure tilts, due to damage to its hull for example. If the height of the launch ramp above sea level is too high, the lifeboat may be damaged during its launch. If the height above seal level is too low, the lifeboat may be damaged due to impact by waves and it may become difficult to launch the lifeboat.
Offshore installations, such as oil platforms, may be provided with more lifeboats than are necessary for the number of people working on the offshore installation. This is to ensure that there are enough lifeboats for everyone even if some of the lifeboats are rendered unusable/un-reachable (due to a fire in one part of the offshore installation) or un-launchable (due to the offshore installation tilting). Half of an offshore installation's lifeboats may for example be located on one side of the offshore installation and the other half may be located on the opposite side of the offshore installation. Problems may still however arise if all of the offshore installation's lifeboats are unusable/un-reachable or un-launchable.
UK patent application no. GB 2 092 103 discloses an oil platform comprising an extensible support arm that is arranged to swing a lifeboat away from the oil platform. The support arm extends under gravity and a coupling is released to drop the lifeboat into the sea in order to reduce the drop between the life-boat's mooring position and the sea, or to eliminate the drop completely. A disadvantage with such a lifeboat launching system is that it involves high fabrication costs and significant maintenance costs in exchange for a relatively minimal guarantee of functional reliability.